86 THE BIOLOGY OF DAILY LIFE. 



APPENDIX TO CHAPTER VI. 



REMARKS ON THE GENERAL REASONING ON WHICH THE 

 CONCLUSIONS OF THE SPECIFIC MICROBE THEORISTS 

 ARE BASED, AND ON SOME OF THE METHODS EM- 

 PLOYED BY THEM FOR CLASSIFYING AND IDENTIFYING 

 MICRO-ORGANISMS. 



IN the Introduction to Micro-organisms and Disease 

 Dr. Klein lays down four conditions (taken from 

 Koch's Die Milzbrand-impfung) which must be com- 

 plied with before it " can be said to be satisfactorily 

 proved that a particular infectious disease is due to a 

 particular micro-organism." These are given fully on 

 pages two and three of that work. I here give them 

 briefly in my own words. 



The four conditions are that the particular micro- 

 organisms must be 



1. Present in the blood or tissues of the man or 

 animal suffering or dead from the disease. 



2. Cultivated in suitable media outside the body, 

 and so as to be secure from all possible introduction 

 of other micro-organisms during the process of 

 culture. 



3. After having been thus cultivated for several 

 successive generations, they must be introduced into 

 the body of a healthy animal susceptible to the disease, 

 and it must be shown that the animal becomes affected 

 with the particular disease. 



4. And, finally, that in this "so affected new 



